Although early cases of acquired immunodeficiency syndrome (AIDS) in the Western world were large confined to male homosexuals, hemophiliacs, and injecting drug users, increasing numbers of women are becoming infected with human immunodeficiency virus type 1 (HIV-1) through heterosexual intercourse as the epidemic progresses (1). There is evidence to suggest that in women dendritic cells in the cervicovaginal mucosa are the first cells to be infected with the virus following heterosexual exposure (2). After this initial infection, virus is then seeded to lymph nodes and other organs throughout the body. In these sub-compartments, the virus evolves in response to immunological selective pressures. Therefore, over time distinct viral populations evolve within a single individual (3). Although current combination anti-retroviral therapies have been shown to dramatically decrease the viral load in the peripheral blood (4) and lymphoid tissue (5), little is known of efficacies in other compartments. In these studies, we are interested in understanding the genetic relationships between the viral variants in the blood and cervicovaginal secretions of HIV-1-infected women. Specifically, we will perform DNA sequence analysis of the V3 loop of gp120, the viral envelope gene, on peripheral blood and cervicovaginal lavage (CVL) specimens from HIV-1- infected women. This region of the HIV-1 genome is responsible for immune recognition (6) and cellular tropism (7). These results may facilitate achievement of two crucial long-term goals: the design of therapies to prevent AIDS in HIV-1-infected women and development of interventions to better prevent heterosexual and perinatal forms of HIV-1 transmission.